The importance of ambient noise monitoring
Monitoring ambient noise is a crucial step in measuring hearing thresholds accurately. Uncontrolled environmental noise can cause subjects to misinterpret test stimuli, leading to false responses or invalid results. By monitoring ambient noise levels, clinicians and hearing health professionals can mitigate these interferences, leading to better diagnosis and treatment outcomes.
Why measure ambient noise
Any audiometric test is invalid if not conducted in an environment suitably free from ambient (or background) noise. Too much ambient noise can “mask” the pure-tone test signal, making it inaudible to the test subject. This can falsely raise the resulting hearing threshold. Evidence may be required to prove that audiometry has been conducted in an appropriate, noise-free environment. If this cannot be provided, the results of a test should be rejected.
Organisations such as the BSA (British Society of Audiology), ANSI (American National Standards Institute), ISO (International Organization for Standardization), and OSHA (Occupational Safety and Health Administration) outline specific noise level requirements for audiometric testing environments. Measuring ambient noise helps to ensure compliance with these standards.
How to assess and monitor ambient noise
The location in which audiometry is conducted should be assessed and monitored:
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“Assessment” should ensure that sound levels are within specified limits in every third-octave frequency band. This must be conducted with a calibrated class 1 or class 2 sound level meter (SLM) that is able to accurately measure to a sufficiently low sound level in each frequency band. This should be conducted on an appropriate periodic basis, when a new location is used or when noise conditions have changed.
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“Monitoring” should ensure that sound levels have not changed for each test session (e.g. on a daily basis in one location) and may be checked with a broadband sound level meter, i.e. a calibrated meter that gives a single dB(A) reading rather than readings for each frequency-band. Trained staff, competent to undertake audiometry, should also be continually aware of the potential effect of background noise.
What to use for measuring ambient noise
Ambient noise can be measured with a sound level meter or sound room microphone. This measures the frequency content in octave or third-octave bands. It’s important to remember that a certain degree of ‘measurement uncertainty’ exists from sources such as the environment (ambient noise and distractions), equipment, subject, method and tester.
What is an acceptable level of background noise?
The level of acceptable background noise for audiometry is defined by the British Society of Audiology (2025) guidance “Acoustic Considerations for Audiology Clinics”, based on ISO standards. The criteria are based on the ambient noise level in a room and the attenuation of the ambient sound by the headphones used in the test. Supra-aural headphones provide the least attenuation, so noise-reducing headphones may be considered.
Some audiometers are available with a microphone that measures the ambient noise during a hearing test. This is helpful in providing assurance that a test is conducted in suitable conditions. However, these microphones are not class 1 or 2 SLM’s, so can only be used for monitoring sound levels, and cannot replace the need for assessment of the location.
The BSA (2023) “Surveillance Audiometry” guidance states that, “in general, the ambient noise should not exceed 35 dB(A)”. This provides reasonable assurance for monitoring, assuming that the test subject is wearing headphones that provide some attenuation of the ambient noise, but it also does not fulfil the need for assessment of the test environment as defined by the BSA acoustics document (2025).
How to ensure an environment is appropriate for audiometry
It may be a challenge to ensure that non-clinical settings, such as the workplace, meet ambient noise requirements. Nevertheless, it should be remembered that insufficient control of ambient noise can invalidate tests and put the organisation at legal risk if test conditions are later contested.
Levels of noise often fluctuate and, if the noise is fleeting and not frequently intrusive, a test can be momentarily suspended or rescheduled. Any competent person conducting audiometry must be aware of this.
Levels of noise that are close to, but above the stated limits might be acceptable if noise-reducing headphones are used, but the attenuation of the headphones should be known. Noise can also be reduced by installing an audiometry booth in a room. In this case, ambient noise levels should be measured in the booth.
The ambient noise in a test room should be properly assessed and monitored as described above. This should be checked against recommended limits (BSA, 2025). If headphones are used, the attenuation should be known and added to the acceptable noise limit.
Ambient noise monitoring solutions
Adding a Sound Room Microphone (SRM) to your test process allows you to monitor the test environment, providing you with reassurance in the quality of your audiometry results. At Amplivox we offer several solutions that include SRM technology:
The Anova™ delivers unmatched accuracy with the option of an external SRM. The microphone is placed in the test environment, providing live feedback when noise exceeds the ‘ideal level’ for accurate measurements. Enabling you to achieve the best possible test conditions.*
Our modelONE pc-based audiometer consists of noise-attenuating headphones, which includes an in-built SRM.*
For more information about which of our devices include ambient noise level monitoring, please contact our customer support team. You can contact us on +44 (0)1865 880 846 or by email.
